METHOD OF CONTROLLING FREQUENCY CONVERTER AND FREQUENCY CONVERTER TO WHICH THE METHOD IS APPLIED

摘要

PURPOSE: To minimize harmonics by controlling the current of a frequency converter through such modulation as the current modulation interval of each phase crosses the current modulation interval of other phase thereby obtaining a good waveform both for the current and the load current. CONSTITUTION: A control unit 2 modulates both a current being drained from a main power supply by a frequency converter, and a current being fed to a load. The modulation is performed such that the modulation interval of each phase crosses the modulation interval of other two phases. In case of sine wave control currents IRC, ISC and ITC, a positive pulse iR+ controls transistors TrQ1 , Q7 which conduct during positive half cycle and a negative pulse iR- . controls transistors TrQ2 , Q8 which conduct during negative half cycle for the current control signal IRC during phase R. The current control signal ISC for the TrQ3 , Q4 , Q9 and Q10 during phase S and the current control signal ITC for the TrQ5 , Q6 , Q11 and Q12 during phase T serve similarly to the current control signal IRC during phase R.